Browsing by Author "Zhang, Xu"

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    Art Center on the Lake
    Zhang, Xu (Virginia Tech, 2020-02-11)
    The water's shore, used for defense, trade, transportation and industry, always plays an important role in a city's development. Buildings were built there to fulfill related practical functions, such as barns, factories or piers. However, at the present time, the functions mentioned above are not the only purpose of the shore, now more entertainment activies happen along the water's edge. Therefore, architecture's roles are changing. The site is in a small town called Riva San Vitale, which is located at the south end of Lake Lugano, Switzerland. For this small town, lake's shore is usually used by local people as a place for relaxation. Based on my four-month long living experiences there, I decided to design an art center on the lake to enrich residents' daily life.
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    Artificial Neuronal Devices Based on Emerging Materials: Neuronal Dynamics and Applications
    Liu, Hefei; Qin, Yuan; Chen, Hung-Yu; Wu, Jiangbin; Ma, Jiahui; Du, Zhonghao; Wang, Nan; Zou, Jingyi; Lin, Sen; Zhang, Xu; Zhang, Yuhao; Wang, Han (Wiley-V C H Verlag, 2023-03)
    Artificial neuronal devices are critical building blocks of neuromorphic computing systems and currently the subject of intense research motivated by application needs from new computing technology and more realistic brain emulation. Researchers have proposed a range of device concepts that can mimic neuronal dynamics and functions. Although the switching physics and device structures of these artificial neurons are largely different, their behaviors can be described by several neuron models in a more unified manner. In this paper, the reports of artificial neuronal devices based on emerging volatile switching materials are reviewed from the perspective of the demonstrated neuron models, with a focus on the neuronal functions implemented in these devices and the exploitation of these functions for computational and sensing applications. Furthermore, the neuroscience inspirations and engineering methods to enrich the neuronal dynamics that remain to be implemented in artificial neuronal devices and networks toward realizing the full functionalities of biological neurons are discussed.
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    Nonconforming Immersed Finite Element Methods for Interface Problems
    Zhang, Xu (Virginia Tech, 2013-05-04)
    In science and engineering, many simulations are carried out over domains consisting of multiple materials separated by curves/surfaces. If partial differential equations (PDEs) are used to model these simulations, it usually leads to the so-called interface problems of PDEs whose coefficients are discontinuous. In this dissertation, we consider nonconforming immersed "nite element (IFE) methods and error analysis for interface problems. We "first consider the second order elliptic interface problem with a discontinuous diffusion coefficient. We propose new IFE spaces based on the nonconforming rotated Q1 "finite elements on Cartesian meshes. The degrees of freedom of these IFE spaces are determined by midpoint values or average integral values on edges. We investigate fundamental properties of these IFE spaces, such as unisolvency and partition of unity, and extend well-known trace inequalities and inverse inequalities to these IFE functions. Through interpolation error analysis, we prove that these IFE spaces have optimal approximation capabilities. We use these IFE spaces to develop partially penalized Galerkin (PPG) IFE schemes whose bilinear forms contain penalty terms over interface edges. Error estimation is carried out for these IFE schemes. We prove that the PPG schemes with IFE spaces based on integral-value degrees of freedom have the optimal convergence in an energy norm. Following a similar approach, we prove that the interior penalty discontinuous Galerkin schemes based on these IFE functions also have the optimal convergence. However, for the PPG schemes based on midpoint-value degrees of freedom, we prove that they have at least a sub-optimal convergence. Numerical experiments are provided to demonstrate features of these IFE methods and compare them with other related numerical schemes. We extend nonconforming IFE schemes to the planar elasticity interface problem with discontinuous Lam"e parameters. Vector-valued nonconforming rotated Q1 IFE functions with integral-value degrees of freedom are unisolvent with appropriate interface jump conditions. More importantly, the Galerkin IFE scheme using these vector-valued nonconforming rotated Q1 IFE functions are "locking-free" for nearly incompressible elastic materials. In the last part of this dissertation, we consider potential applications of IFE methods to time dependent PDEs with moving interfaces. Using IFE functions in the discretization in space enables the applicability of the method of lines. Crank-Nicolson type fully discrete schemes are also developed as alternative approaches for solving moving interface problems.
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    Reduced Firing of Nucleus Accumbens Parvalbumin Interneurons Impairs Risk Avoidance in DISC1 Transgenic Mice
    Zhou, Xinyi; Wu, Bifeng; Liu, Wenhao; Xiao, Qian; He, Wei; Zhou, Ying; Wei, Pengfei; Zhang, Xu; Liu, Yue; Wang, Jie; He, Jufang; Zhang, Zhigang; Li, Weidong; Wang, Liping; Tu, Jie (2021-06-18)
    A strong animal survival instinct is to approach objects and situations that are of benefit and to avoid risk. In humans, a large proportion of mental disorders are accompanied by impairments in risk avoidance. One of the most important genes involved in mental disorders is disrupted-in-schizophrenia-1 (DISC1), and animal models in which this gene has some level of dysfunction show emotion-related impairments. However, it is not known whether DISC1 mouse models have an impairment in avoiding potential risks. In the present study, we used DISC1-N terminal truncation (DISC1-N-TM) mice to investigate risk avoidance and found that these mice were impaired in risk avoidance on the elevated plus maze (EPM) and showed reduced social preference in a three-chamber social interaction test. Following EPM tests, c-Fos expression levels indicated that the nucleus accumbens (NAc) was associated with risk-avoidance behavior in DISC1-N-TM mice. In addition, in vivo electrophysiological recordings following tamoxifen administration showed that the firing rates of fast-spiking neurons (FS) in the NAc were significantly lower in DISC1-N-TM mice than in wild-type (WT) mice. In addition, in vitro patch clamp recording revealed that the frequency of action potentials stimulated by current injection was lower in parvalbumin (PV) neurons in the NAc of DISC1-N-TM mice than in WT controls. The impairment of risk avoidance in DISC1-N-TM mice was rescued using optogenetic tools that activated NAcPV neurons. Finally, inhibition of the activity of NAcPV neurons in PV-Cre mice mimicked the risk-avoidance impairment found in DISC1-N-TM mice during tests on the elevated zero maze. Taken together, our findings confirm an impairment in risk avoidance in DISC1-N-TM mice and suggest that reduced excitability of NAcPV neurons is responsible.